Neighbor Discovery for IP Version 6 (IPv6)
RFC 2461

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Network Working Group                                        T. Narten
Request for Comments: 2461                                         IBM
Obsoletes: 1970                                            E. Nordmark
Category: Standards Track                             Sun Microsystems
                                                            W. Simpson
                                                            Daydreamer
                                                         December 1998

               Neighbor Discovery for IP Version 6 (IPv6)

Status of this Memo

   This document specifies an Internet standards track protocol for the
   Internet community, and requests discussion and suggestions for
   improvements.  Please refer to the current edition of the "Internet
   Official Protocol Standards" (STD 1) for the standardization state
   and status of this protocol.  Distribution of this memo is unlimited.

Copyright Notice

   Copyright (C) The Internet Society (1998).  All Rights Reserved.

Abstract

   This document specifies the Neighbor Discovery protocol for IP
   Version 6.  IPv6 nodes on the same link use Neighbor Discovery to
   discover each other's presence, to determine each other's link-layer
   addresses, to find routers and to maintain reachability information
   about the paths to active neighbors.

   Table of Contents

   1.  INTRODUCTION.............................................    3
   2.  TERMINOLOGY..............................................    4
      2.1.  General.............................................    4
      2.2.  Link Types..........................................    7
      2.3.  Addresses...........................................    8
      2.4.  Requirements........................................    9
   3.  PROTOCOL OVERVIEW........................................    9
      3.1.  Comparison with IPv4................................   13
      3.2.  Supported Link Types................................   15
   4.  MESSAGE FORMATS..........................................   17
      4.1.  Router Solicitation Message Format..................   17
      4.2.  Router Advertisement Message Format.................   18
      4.3.  Neighbor Solicitation Message Format................   21
      4.4.  Neighbor Advertisement Message Format...............   23
      4.5.  Redirect Message Format.............................   26

Narten, et. al.             Standards Track                     [Page 1]
RFC 2461              Neighbor Discovery for IPv6          December 1998

      4.6.  Option Formats......................................   28
         4.6.1.  Source/Target Link-layer Address...............   28
         4.6.2.  Prefix Information.............................   29
         4.6.3.  Redirected Header..............................   31
         4.6.4.  MTU............................................   32
   5.  CONCEPTUAL MODEL OF A HOST...............................   33
      5.1.  Conceptual Data Structures..........................   33
      5.2.  Conceptual Sending Algorithm........................   35
      5.3.  Garbage Collection and Timeout Requirements.........   37
   6.  ROUTER AND PREFIX DISCOVERY..............................   37
      6.1.  Message Validation..................................   38
         6.1.1.  Validation of Router Solicitation Messages.....   38
         6.1.2.  Validation of Router Advertisement Messages....   39
      6.2.  Router Specification................................   40
         6.2.1.  Router Configuration Variables.................   40
         6.2.2.  Becoming An Advertising Interface..............   44
         6.2.3.  Router Advertisement Message Content...........   44
         6.2.4.  Sending Unsolicited Router Advertisements......   46
         6.2.5.  Ceasing To Be An Advertising Interface.........   46
         6.2.6.  Processing Router Solicitations................   47
         6.2.7.  Router Advertisement Consistency...............   48
         6.2.8.  Link-local Address Change......................   49
      6.3.  Host Specification..................................   50
         6.3.1.  Host Configuration Variables...................   50
         6.3.2.  Host Variables.................................   50
         6.3.3.  Interface Initialization.......................   51
         6.3.4.  Processing Received Router Advertisements......   51
         6.3.5.  Timing out Prefixes and Default Routers........   54
         6.3.6.  Default Router Selection.......................   54
         6.3.7.  Sending Router Solicitations...................   55
   7.  ADDRESS RESOLUTION AND NEIGHBOR UNREACHABILITY DETECTION.   56
      7.1.  Message Validation..................................   57
         7.1.1.  Validation of Neighbor Solicitations...........   57
         7.1.2.  Validation of Neighbor Advertisements..........   58
      7.2.  Address Resolution..................................   58